A power converter is conventionally provided with a switching element, which is used for converting a direct current. That is, a power converter may convert a direct current (DC) power source to an alternating current (AC) power source and output a voltage different than the input voltage (i.e. a different electric potential) by turning ON and OFF the switching element with a DC power source when the switching element is in the high side configuration. Such a power converter may use a switching element such as an N-channel type (n-type) Metal Oxide Semiconductor Field Effect Transistor (MOSFET) having a high capacity. In such case, when the MOSFET is driven on the high-side, the source voltage of the MOSFET (i.e. voltage at the MOSFET source) rises to a voltage of a power source after turning ON, with the MOSFET gate requiring a voltage higher than the voltage of the power source for proper operation.
Accordingly, a booster circuit, such as a charge pump circuit or the like, may be used in the above-described circumstance. Further, since the driving capacity provided by the charge pump circuit alone may be insufficient in cases where there is a drop in power source voltage, a bootstrap circuit may be added in some configurations.
However, when used in a vehicle with an in-vehicle battery as the DC power source, a power converter may suffer from fluctuating terminal voltage due to other loads powered by the battery. In cases where a DC source battery rises to excessively high voltage levels, the resulting high voltage in the bootstrap circuit may cause damage or failure to the MOSFET's gate drive circuit.
(Patent document 1) Japanese Patent Laid-Open No. 2014-11841